Ammonia, urea, and metals are species that are commonly presented in wastewater that is derived from different sources, e.g., industrial, livestock, ships, hydrometallurgy, electronics, and the like.
There are different processes that allow the removal of these species individually, including for example, chemical precipitation, ion exchange, reverse osmosis, surface clay filtration, electrowinning, electrodialysis, air/steam stripping, anaerobic biological oxidation/nitrification, and breakpoint chlorination. However, none of these processes provide the capability of performing the removal of the aforementioned species simultaneously. Moreover, the required regulatory limits or the desired low levels cannot be achieved efficiently.
For example, electrowinning may be used for the removal of metal ions in aqueous solutions. And while electrowinning can recover 90 to 95% of the available metal ions, it is known to operate efficiently only at high metal on concentrations. For example, as the concentration of the metal ions decrease to lower concentrations, such as about 500 mg/L (parts per million or ppm) or less, higher voltages and/or current densities must be used. At these low concentration conditions, the excess electrical energy is diverted into producing hydrogen at the cathode, which thereby competes with the reduction of the metal. Moreover, a substantial amount of energy is consumed by the hydrogen generation. As such, as the low levels required by regulatory agencies, such as the Environmental Protection Agency, are approached, the process becomes increasingly less efficient.
Further, anaerobic biological oxidations may be used for the removal of ammonia. However, these methods require a strict control of the pH to keep the bacteria alive, and require long retention times. Moreover, these processes have not been shown to be applicable for the removal of metals from waste water.
Osmosis can be used to filter water from impurities, but it does not ultimately remove the impurities and instead merely concentrates them. In addition, removal of ammonia by this process requires expensive membranes and high pressure.
Therefore, a need still exists for an efficient and simultaneous method for removing metals, and urea and/or ammonia from waste water.